The Experts below are selected from a list of 171 Experts worldwide ranked by ideXlab platform

Paul A Madden - One of the best experts on this subject based on the ideXlab platform.

  • simulation of pressure driven phase transitions from Tetrahedral Crystal structures
    Physical Review B, 2002
    Co-Authors: Mark R Wilson, Francis Hutchinson, Paul A Madden
    Abstract:

    Pressure-driven transitions of ionic materials from the zinc-blende to rocksalt and δ-ZnCl 2 to CdCl 2 Crystal structures are studied using constant-stress molecular dynamics with a polarizable-ion potential model. Both transformations are characterized by a change in cation coordination environment from Tetrahedral to octahedral and are nonmartensitic. Transformation mechanisms are identified and characterized and similarities discussed. The blende to rocksalt transformation is observed to proceed via a diatomic β-tin-like structure, though this is shown to be a transition state and not a true intermediate phase in this system. The relationship of the observed mechanisms to those deduced from experiments on halide systems is discussed. The development of displacive motion across the simulation cell is discussed. The ZnCl 2 system is a layered structure, and while the coordination changes are highly cooperative within each layer, the overall transformation takes place on a layer-by-layer basis. In the blende, the interlayer correlations required to produce a grain-boundary-free final structure are associated with a shearing motion which propagates across the cell. These differences have characteristic effects on the kinetics of the transformations.

Mark R Wilson - One of the best experts on this subject based on the ideXlab platform.

  • simulation of pressure driven phase transitions from Tetrahedral Crystal structures
    Physical Review B, 2002
    Co-Authors: Mark R Wilson, Francis Hutchinson, Paul A Madden
    Abstract:

    Pressure-driven transitions of ionic materials from the zinc-blende to rocksalt and δ-ZnCl 2 to CdCl 2 Crystal structures are studied using constant-stress molecular dynamics with a polarizable-ion potential model. Both transformations are characterized by a change in cation coordination environment from Tetrahedral to octahedral and are nonmartensitic. Transformation mechanisms are identified and characterized and similarities discussed. The blende to rocksalt transformation is observed to proceed via a diatomic β-tin-like structure, though this is shown to be a transition state and not a true intermediate phase in this system. The relationship of the observed mechanisms to those deduced from experiments on halide systems is discussed. The development of displacive motion across the simulation cell is discussed. The ZnCl 2 system is a layered structure, and while the coordination changes are highly cooperative within each layer, the overall transformation takes place on a layer-by-layer basis. In the blende, the interlayer correlations required to produce a grain-boundary-free final structure are associated with a shearing motion which propagates across the cell. These differences have characteristic effects on the kinetics of the transformations.

Andreas Eling - One of the best experts on this subject based on the ideXlab platform.

  • Molecular recognition among alcohols and amines: super-Tetrahedral Crystal architectures of linear diphenol–diamine complexes and aminophenols
    Journal of The Chemical Society-perkin Transactions 1, 1994
    Co-Authors: Otto Ermer, Andreas Eling
    Abstract:

    Hydroxy and amino groups are complementary as regards hydrogen-bond donors and acceptors. This is expected to lead to molecular recognition among alcohols and primary amines, i.e., to a propensity towards formation of 1 : 1 alcohol–amine complexes, driven by a 50% increase of the number of hydrogen bonds as compared with the uncomplexed constituents. Possible hydrogen-bonded architectures of such complexes are suggested, and the concept is successfully exploited for Crystal engineering purposes by drawing upon linear diphenols, aromatic diamines, and aminophenols as supramolecular partners. Specifically, the Crystal-structural chemistry is reported of the 1 : 1 molecular complexes between hydroquinone and p-phenylenediamine, hydroquinone and benzidine, 4,4′-dihydroxybiphenyl and p-phenylenediamine, 4,4′-dihydroxybiphenyl and benzidine, as well as of p-aminophenol, and of 4,4′-hydroxyaminobiphenyl. The diphenol–diamine complexes form hyderogen-bonded super-diamond lattices with 1.5 O(H) N bonds per oxygen and nitrogen atoms, respectively. Again exclusively via O(H)N bonds, the aminophenol structures are also superTetrahedral but after the manner of the polar wurtzite variant. Some similar reported structures are analysed in the light of the present concepts and results, and implications are discussed of the finding that molecular recognition is possible among molecules as standard as simple alcohols and amines.

  • molecular recognition among alcohols and amines super Tetrahedral Crystal architectures of linear diphenol diamine complexes and aminophenols
    Journal of The Chemical Society-perkin Transactions 1, 1994
    Co-Authors: Otto Ermer, Andreas Eling
    Abstract:

    Hydroxy and amino groups are complementary as regards hydrogen-bond donors and acceptors. This is expected to lead to molecular recognition among alcohols and primary amines, i.e., to a propensity towards formation of 1 : 1 alcohol–amine complexes, driven by a 50% increase of the number of hydrogen bonds as compared with the uncomplexed constituents. Possible hydrogen-bonded architectures of such complexes are suggested, and the concept is successfully exploited for Crystal engineering purposes by drawing upon linear diphenols, aromatic diamines, and aminophenols as supramolecular partners. Specifically, the Crystal-structural chemistry is reported of the 1 : 1 molecular complexes between hydroquinone and p-phenylenediamine, hydroquinone and benzidine, 4,4′-dihydroxybiphenyl and p-phenylenediamine, 4,4′-dihydroxybiphenyl and benzidine, as well as of p-aminophenol, and of 4,4′-hydroxyaminobiphenyl. The diphenol–diamine complexes form hyderogen-bonded super-diamond lattices with 1.5 O(H) N bonds per oxygen and nitrogen atoms, respectively. Again exclusively via O(H)N bonds, the aminophenol structures are also superTetrahedral but after the manner of the polar wurtzite variant. Some similar reported structures are analysed in the light of the present concepts and results, and implications are discussed of the finding that molecular recognition is possible among molecules as standard as simple alcohols and amines.

Francis Hutchinson - One of the best experts on this subject based on the ideXlab platform.

  • simulation of pressure driven phase transitions from Tetrahedral Crystal structures
    Physical Review B, 2002
    Co-Authors: Mark R Wilson, Francis Hutchinson, Paul A Madden
    Abstract:

    Pressure-driven transitions of ionic materials from the zinc-blende to rocksalt and δ-ZnCl 2 to CdCl 2 Crystal structures are studied using constant-stress molecular dynamics with a polarizable-ion potential model. Both transformations are characterized by a change in cation coordination environment from Tetrahedral to octahedral and are nonmartensitic. Transformation mechanisms are identified and characterized and similarities discussed. The blende to rocksalt transformation is observed to proceed via a diatomic β-tin-like structure, though this is shown to be a transition state and not a true intermediate phase in this system. The relationship of the observed mechanisms to those deduced from experiments on halide systems is discussed. The development of displacive motion across the simulation cell is discussed. The ZnCl 2 system is a layered structure, and while the coordination changes are highly cooperative within each layer, the overall transformation takes place on a layer-by-layer basis. In the blende, the interlayer correlations required to produce a grain-boundary-free final structure are associated with a shearing motion which propagates across the cell. These differences have characteristic effects on the kinetics of the transformations.

P.c. Ball - One of the best experts on this subject based on the ideXlab platform.

  • The group theory of trigonal and Tetrahedral molecule rotations in trigonal and Tetrahedral Crystal fields
    Molecular Physics, 1990
    Co-Authors: M.v. Smalley, P.c. Ball
    Abstract:

    The permutation symmetry groups introduced by Longuet-Higgins are employed to solve the group theory for molecules of C3v and Td symmetry rotating in Crystal fields of C3v and Td symmetry. The qualitative appearances of the energy level diagrams for the groups (C3v, [Cbar]3v), (C3v, [Tbar]d) and (Td, [Cbar]3v) are deduced for the range of barrier heights from the free-rotor limits to the pinned limits, for the ground state multiplet only. The correlations between the groups derived here and the group (Td, [Tbar]d) treated by Miller and Decius are considered and the alteration in the ground state splitting pattern in going from a Tetrahedral molecule in a Tetrahedral field through to a trigonal molecule in a trigonal field is illustrated. The group (C3v, [Cbar]3v) is treated in detail and applied to the tunnelling states of monodeuteromethane adsorbed on the surface of graphite. The rotational Hamiltonian matrix is constructed in the pocket state formalism and diagonalized using the character table for (C3...